The Islamic State jihadist group on Sunday claimed to have executed Peter Kassig, a US aid worker kidnapped in Syria, as a warning to the United States.
The same video showed the gruesome simultaneous beheadings of at least 18 men described as Syrian military personnel, the latest in a series of mass executions and other atrocities carried out by IS.
"This is Peter Edward Kassig, a US citizen of your country," said a black-clad militant wearing a balaclava, the same outfit worn by the man who beheaded two American journalists and two British aid workers in earlier videos.
The man stood over a severed head bearing a resemblance to Kassig, a former American soldier who risked his life to provide medical treatment and aid to those suffering from Syria's civil war.
Kassig, a 26-year-old from Indiana who was kidnapped in 2013 in Syria's Deir Ezzor province, also worked in hospitals and clinics treating Syrians who fled to neighbouring Turkey and Lebanon.
He wrote to his parents saying: "If I do die, I figure that at least you and I can seek refuge and comfort in knowing that I went out as a result of trying to alleviate suffering and helping those in need."
The militant in the video made no mention of Kassig's aid work, only referring to his time as a US soldier in Iraq.
"Here, we are burying the first American crusader in Dabiq, eagerly waiting for the remainder of your armies to arrive," the militant said.
Dabiq is the site of a major 16th century battle in what is now northern Syria that saw the Ottomans defeat the Mamluks and begin a major expansionist phase of an empire the IS group considers to have been the last caliphate.
In a highly choreographed sequence earlier in the video, jihadists marched at least 18 prisoners said to be Syrian officers and pilots past a wooden box of long black military knives, each taking one as they passed, then forced them to kneel in a line and decapitated them.
"Today, we're slaughtering the soldiers of Bashar," the same black-clad militant said, referring to Syrian President Bashar al-Assad.
"Tomorrow, we'll be slaughtering your (US) soldiers. And with Allah's permission, we will break this final and last crusade, and the Islamic State will... begin to slaughter your people on your streets."
IS spearheaded a militant offensive that overran much of Iraq's Sunni Arab heartland since June after seizing major territory in neighbouring Syria, and carried out a series of atrocities in both countries.
The group has killed hundreds of Iraqi and Syrian tribesmen who opposed it, attacked religious and ethnic minorities, sold women as slaves, executed scores of Iraqi security personnel and carried out beheadings on camera.